An apparatus of the above-discussed type is disclosed in U.S. patent application Ser. No. 194,397 filed on Oct. 6, 1980, in the names of Olof Engstrom and Christer Ovren, and assigned to a common assignee with the present application, (the disclosure of which is incorporated herein by reference). This U.S. patent application describes a device in which light is conducted via at least one optic fiber towards a material which is in optical contact with the fiber and which has temperature-dependent luminescent properties, whereby luminescence occurs. The light thus emitted is conducted via at least one optic fiber, possibly wholly or partially in common with the above-mentioned fiber, to an electronic measuring means. The material consists of a semiconductor material with temperature-dependent luminescence. This principle of temperature measurement involves a reliable, economical and robust measuring apparatus, which can be used with advantage in difficult environments or environments which are difficult to reach, for example where there are strong electric fields.
The references to "light" in this specification should be taken to include electromagnetic radiation which is not necessarily in the visible region of the spectrum, and references to "photo-luminescence", "photo-diode" and "light-emitting diode" (or "LED") should also be taken to include properties and devices operating in regions outside the visible spectrum.
The present invention represents an improvement of the above-mentioned concept, where it is desired to determine temperatures at a plurality of locations while at the same time reducing the considerable costs associated with the provision of a separate electronic measuring means (with its electronic and optical equipment) for each measuring location. It has proved difficult to find a fiber optical solution to this problem, but the present invention provides such a solution.